@ Carnifex: there is a finished version as well. It's in the same resolution as this one...but finished. Glad you liked this!
And here is another city made with the same technigue:
Oh my goodness, this is a beautiful city map indeed! :) I cannot wait to see further progress. I love the look of the forest and trees in general, by the way. Is it the same tree over and over? Or had you created groups of trees before making the forest?
@ Renacido: this map is actually already finished, you can find the link above. The trees are actually a simple texture (the one attached) and I just paint with it using standard Photoshop soft round brush. I have applied bevel and drop shadow to the forest layer to make them pop out properly.